The Physicians of Myddfai (Welsh: Meddygon Myddfai) were, according to local folklore, a succession of physicians who lived in the parish of Myddfai in Carmarthenshire, Wales.
The folklore places their first appearance in the 13th century, when Rhiwallon the Physician and his three sons were doctors to Rhys Gryg, prince of Deheubarth. It was said that they treated Rhys when he was wounded in battle near Carmarthen in 1234, but he died of his wounds shortly afterwards at Llandeilo. The family are supposed to have continued to follow the profession in the direct male line until 1739, when John Jones, the last of the line of physicians, died. Instructions for preparing herbal medicine attributed to the family have survived in the Red Book of Hergest, which dates from the late 14th century, and in other, more recent, Welsh manuscripts.